It is proposed here and elsewhere that cytosolic alkaline ribonuclease--ribonuclease inhibitor systems might be involved with extra-nuclear processing of mRNA-containing the molecular basis for the interactions among alkaline ribonuclease, ribonuclease inhibitors and RNA. The purpose of this research project is to examine, in detail, those interactions using alkaline ribonuclease, ribonuclease inhibitor and RNA all from the same tissue, porcine thyroid. We plan on purifying thyroid alkaline ribonuclease and ribonuclease inhibitor to homogeneity and then after characterization to study the mechanism of the interactions involved between the proteins and among them and various species of RNA using protein and nucleic acid chemical modifications, physical techniques and kinetic analyses. An assay for ribonuclease activity measurements we have recently developed should significantly aid these investigations. The proposed research is intended to lay a foundation upon which the system's postulated role in RNA processing can, in subsequent studies, be examined in a tissue which is amenable to more physiological approaches to the examination of the regulation of extra-nuclear RNA metabolism.